Chemical Biological air-purifying filtration devices such as those currently used by U.S. joint force and homeland security personnel employ multiple layers of filter media to provide protection against a wide range of aerosol and chemical threat agents. One or more layers typically contain a fibrous medium that traps particulate threats of biological origin (e.g., bacteria, viruses, and toxins) and other harmful aerosols by inertial impaction, diffusion, and/or electrostatic attraction. Another layer typically contains a sorbent material such as a bed of activated carbon to capture gaseous toxic vapors by physical adsorption. To remove high volatility toxic vapors that are not retained on activated carbon by physical adsorption the adsorbent layer is often impregnated with a reactive chemical that breaks down the vapor into more benign chemical compounds that can be adsorbed.
One significant challenge in designing a Chemical Biological air-purifying filtration device is to provide protection against a wide range of contaminants for a reasonable period of time without imposing a burdensome breathing resistance on the user and without adding to filter bulkiness, weight, or air-purifying system complexity. For example, filter cartridges used in the M50 dual cartridge Chemical Biological respirator, widely deployed by U.S. joint forces, are about 2.5 cm in depth and provide a combined filter surface area of 125 cm2. Carbon adsorbent beds in the filter cartridges are about 10 to 15 mm deep. A relatively deep carbon bed depth is needed to avoid early breakthrough of toxic vapors that are injected at relatively high linear velocity in filters of this surface area. Aerosol filter media also needs to be about 10 to 15 mm deep to trap smaller particles of concern. While the twin filter design of the M50 is highly effective and represents a significant improvement over previous designs, breathing resistance provided by twin filter masks such as the M50 can cause premature fatigue and user discomfort, especially in operations where users are under significant physical or mental stress.
Incorporating larger filters in conventional chemical biological respirator masks intended for use by military and law enforcement personnel has been especially difficult. These difficulties include obstructing the wearer's field of vision, adding weight and bulk to already burdensome headgear and restricting movement of the head. For the reasons stated above and for additional reasons stated hereinafter, which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need for an improved Chemical Biological air-purifying filter that provides reduced breathing resistance without increasing the overall size of a filter cartridge or module.